1. Field of the Invention
The present invention relates to semiconductor integrated circuits and, in particular, to a polysilicon fuse trim read cell that utilizes a fuse structure which, when blown, allows the cell to be read and its value retained as a digital output. The cell uses no power in the steady state.
2. Discussion of the Related Art
The increasing use of handheld and portable electronic devices is driving the need for power management in the operation of the integrated circuits utilized in these devices.
Many electronic systems incorporate a bandgap circuit that generates a reference voltage that is used for operation of other circuits in the system. The bandgap circuit is typically xe2x80x9ctrimmedxe2x80x9d during its testing to adjust the circuit to compensate for the impact of environmental effects, e.g. ambient temperature, during operation. The trimmed bandgap circuit is more reliable in providing a nonvariable reference voltage.
In one technique for trimming a bandgap circuit, a digital control signal is provided to a variable resistor structure in the bandgap circuit. The selected value of the control signal sets the resistance and, thus, adjusts the operation of the bandgap circuit. The control signal is generated by a trim circuit that draws current during its operation and, therefore, can drain the battery of handheld and portable devices.
A preferred embodiment of the present invention provides a single bit trim read cell that utilizes a polysilicon fuse which, when blown, allows the cell to be read and its stored value to be retained, but which uses no power in the steady state. The fuse is either blown or not blown at circuit test. The trimpad is then used to program an associated single bit storage cell, such as a flip-flop, through a transmission gate that is activated by an input read signal during power up. The data output of the storage cell may be used, for example, as one bit of a multibit programming control signal used in trimming a bandgap reference generator circuit; the remaining bits of the control signal may be provided by similar trim read cell circuits.